Generally, optoelectronic integrated circuit chips typically incorporate a variety of optical devices in addition to electronic devices (e.g., complimentary metal oxide semiconductor (CMOS) devices or other electronic devices). One exemplary optical device is a photodetector (also referred to herein as a photosensor or an optical receiver) made up of a layer of a light-absorbing material and one or more photodiodes (e.g., PN diodes or PIN diodes) within the light-absorbing material. The photodetector receives optical signals (i.e., light) from an optical waveguide (e.g., a silicon waveguide) and converts the optical signals into electronic signals (i.e., electrical current) for processing by one or more of the electronic devices. Exemplary light-absorbing materials can include, but are not limited to, silicon, germanium, indium gallium arsenide, lead sulfide and mercury cadmium telluride. These different light-absorbing materials absorb light in different wavelength ranges. Germanium, for example, absorbs light in the infrared wavelength bands (e.g., 700 nm-1 mm) and is commonly used in silicon photonics for receiving light from optical fibers or other on-chip light sources and converting the light to an electrical current at the frequency of modulation.
Unfortunately, current techniques for forming a germanium photodetector often result in the germanium layer having defects and, particularly, cracks and/or surface pits. Such techniques also do not allow for selective control of the dopant profiles within the diffusion regions of the PIN diodes. Defects and/or inadequate dopant profiles can result in a significant amount of undesirable dark current flowing through the photodetector. Those skilled in the art will recognize that the term “dark current” refers to electric current that flows through an optical device, such as a photodetector, in the absence of photons. There is a need in the art for an improved method of forming a photodetector (e.g., a germanium photodetector) with minimal dark current.